Thursday, September 24, 2009

Directivity is the ratio of radiation intensity to the radiation intensity averaged over a sphere.It is different from gain although both terms are used interchangeably. Directivity is also different from beamwidth and is calculated using the beamwidth angles at half-power as follows,

The Poynting vector is used to define power patterns in electromagnetic waves. It points in the direction of the wave propagation and its amplitude is calculated by multiplying the amplitudes of the electric and magnetic fields divided by the permeability of the medium in which the wave flows.

S = 1/u * EB

where

S is the Poynting vector amplitude

E = the electric field amplitudeB = the magnetic field amplitudeu = the permeability of the medium (4*PI* 10^-7 H/m for vacuum)